1. Field of the Invention
The present invention relates to an integrated circuit (IC) socket and, more specifically, to an IC socket and an IC package mounting device used for mounting an IC package onto a printed circuit board.
2. Description of the Related Art
Techniques for mounting an IC package such as a central processing unit (CPU) or a large scale integrated circuit (LSI) onto a printed circuit with a socket have long been studied. IC sockets for mounting CPUs in land grid array (LGA) packages or ball grid array (BGA) packages are embedded in many personal computers and mother boards.
To improve functions and performances of CPUS, the number of pins and the processing speed have been increasing. With the increase in the number of pins and the processing speed of CPUS, IC packages have been improved to have a larger size and finer pitch and IC sockets have also been improved similarly, in order to support such CPUs having an increased number of pins. The increase in size of an IC package for supporting the increased number of pins increases the flexible volume of the IC package and variations in the height of contact lands and balls thereof. Accordingly, an IC socket also needs to correspond to these increases, and is required to have a structure capable of securing contact strokes of the IC socket. Meanwhile, support for the finer pitch should be achieved with the simplest structure possible, and a desirable structure is one in which an IC package is connected to a printed circuit board at a short distance. Moreover, for the increase in the speed of a CPU, it is important that a contact has low inductance. Here, it is also expected to achieve a high allowable current in response to an increase in a consumption current attributable to the higher speed.
The mainstream of a socket for a LGA package today is one corresponding to 400 to 800 pins at a pitch of about 1 mm with a structure in which given shapes of contacts are formed by intricately bending a metal plate, so that the contacts are inserted into a housing of the IC socket.
However, the structure configured to insert the contacts into the housing of the IC socket employs plate springs. Accordingly, when the lengths of springs are increased to increase strokes of the IC contacts, the springs may touch neighboring pins. In other words, the IC socket has a problem that it is not possible to increase the contact strokes as the pitch becomes finer.
As a countermeasure for increasing contact strokes even in the case of a finer pitch, there is a disclosure in which torsion springs are used for contacts. When torsion springs are used for contacts, it is possible to adjust various parameters such as a wire diameter, an average winding radius, an effective winding number or an arm length in order to achieve required moment and strokes within an allowable stress range determined by a material. Accordingly, the torsion springs provide more design freedom than the simple plate springs and are likely to meet required mechanical characteristics.
Nevertheless, as for an electric characteristic in the case of using the torsion spring as the contact, the torsion spring may be an obstacle to high-speed operation of an IC due to high inductance caused by a coiled structure of the torsion spring.